(a) Field of the Invention
The present invention relates to a biodegradable and thermosensitive poly(organophosphazene) with a functional group, a preparation method thereof, and a use thereof for delivery of bioactive substances.
According to the present invention, poly(organophosphazene) is a phosphagen-based polymer showing biodegradability, thermosensitivity, and sol-gel phase transition depending on temperature change, whereby when administered with bioactive substances, such as drugs, into a living body, the poly(organophosphazene) forms a gel-phase at body temperature capable of controlled release of the bioactive substances. Further, the poly(organophosphazene) has functional groups to chemically bind with the bioactive substances through an ionic bond, covalent bond, or coordinate covalent bond to be capable of a sustained release of the bioactive substances due to its good binding property. Therefore, the poly(organophosphazene) is useful as a delivery material for bioactive substances.
(b) Description of the Related Art
An aqueous solution of a thermosensitive polymer hydrogel can maintain sol-phase at low temperature, and can be changed into gel-phase by raising the temperature.
Such sol-gel phase transition can occur reversibly. Thermosensitive polymer hydrogel has been considered as a useful delivery material of drugs for injection due to its advantages that the aqueous solution thereof can be easily mixed with therapeutic drugs. Therefore, it can be easily injected into a living body without any surgical operation, and when injected into a desired region of a living body, it forms a gel-phase with a three-dimensional structure at body temperature and is thereby capable of controlled and sustained release of the drugs (Nature, 388, 860 (1997), and U.S. Pat. No. 6,201,072).
However, when such thermosensitive polymer hydrogel is used as a delivery material of a drug for injection, there is a problem that drugs with small molecular weights or high hydrophilicity is that they can easily and rapidly pass through the three-dimensional network structure of the gel formed by the thermosensitive polymer hydrogel, causing a large amount of 30% or more of the drugs to be released at an early-stage of the injection. Further, there is another problem that the release of the drug is completed in a short time due to a high rate of diffusion of a hydrophilic drug from the gel into the living body, whereby a sustained release of the drug cannot be achieved (Adv Drug Deliv Rev, 31, 197 (1998)).
In order to solve such problems, various thermosensitive polymer hydrogels with a functional group capable of directly binding to drugs have been developed. When the thermosensitive polymer hydrogel is injected into a living body together with a hydrophilic drug chemically binding thereto through the functional group, the drug is released by degradation of the polymer or breakage of the chemical bond between the polymer and the drug, thereby achieving a sustained release.
It has been tried to bind N-isopropylacrylamide, which is an exemplary thermosensitive polymer, an acrylic acid copolymer that acts as a functional group, and a hydrophilic drug through a direct chemical bond. However, there is still a problem that the N-isopropylacrylamide and the acrylic acid copolymer, which bind with the drug, are cytotoxic and non-biodegradable (Macromolecules, 34, 8569, 2001).
Polyethylene oxide-polylacticglycolic acid-polyethylene oxide (PEO-PLGA-PEO, Regel) is an exemplary thermosensitive polymer hydrogel which is biodegradable in a living body. However, since the PEO-PLGA-PEO polymer has no functional group, it is not able to bind with hydrophilic drugs.
It has also been considered to chemically bind hydrophilic drugs to chitosan with a functional group to form another biodegradable and thermosensitive polymer hydrogel. However, there are still some problems in that it is difficult for chitosan to form a strong chemical bond with hydrophilic drugs due to its insolubility in an organic solvent, and it has a slow gelation rate and low gel solidity, which is undesirable for use as a delivery material of drugs.
The present inventors have reported that poly(organophosphazene)s prepared by substitution with an amino acid ester and methoxypolyethyleneglycol in a linear dichlorophosphazene molecule show a thermosensitivity that has a sol-phase in an aqueous solution at a specific temperature or lower, and a phase transition from the sol-phase to the gel-phase of a three-dimensional structure occurs with raising the temperature above the specific temperature. Further, they are gradually hydrolyzed in an aqueous solution. [Macromolecules 32, 2188 (1999); Macromolecules 32, 7820 (1999); Macromolecules 35, 3876 (2002); Korean Patent Nos. 259,367, and 315,630; and U.S. Pat. No. 6,319,984].
However, the poly(organophosphazene)s disclosed in the above documents have a limitation in being applied as a delivery material of hydrophilic drugs since they have no functional group. Therefore, in order to solve the above problems, it is required to develop novel poly(organophosphazene)s that show a sol-gel phase transition depending on a change of temperature and have a functional group capable of binding with bioactive substances.